Transgender is an umbrella term used to refer to individuals whose gender identity and/or gender expression do not align with what is typically socially ascribed for their biological sex (e.g., a person who is biologically female but identifie as a man). The transgender population encounters a number of health disparities, including elevated levels of mental illness, substance use, and HIV risk. These co-occurring epidemics, also known as a syndemic, may be explained by experiencing elevated rates of minority stressors, including discrimination, harassment, victimization, identity concealment, and internalized transphobia (or a negative self-view related to one's transgender identity). Research with this population has been limited and most studies combine transgender participants (often extremely small samples) with lesbian, gay, and bisexual samples, which ignores the distinct experiences of transgender men and women. Additionally, research has yet to longitudinally explore how these epidemics relate to each other to reveal insights into how the syndemic is produced in this population. To address the dearth of research in this area, a two phase study will be completed. Due to the limited data available, a transgender community advisory board will be convened in Phase 1 of the study, whose aim will be to assure cultural relevance of all aspects of research and inform the daily diary study. This is particularly important given the limited data available and the fact that research may be overlooking critical components of minority stress that the advisory committee will elucidate. In Phase 2, the daily diary study, the specific aims are: 1) elucidate the relations between HIV risk and elevated levels of substance use, minority stress, and psychological distress; 2) identify social/interpersonal (isolation and gender affirmation - gaining social recognition of one's gender identity) and psychological/cognitive mechanisms (rumination and internalized transphobia) that link minority stress, specifically enacted stigma (discrimination, harassment, victimization) to risky sexual behaviors, increased substance use, and psychological distress; and 3) explore gender and racial differences in the above described aims. In Phase 2 of the study, a 2 month daily diary design will be implemented with a sample of transgender men and transgender women. During Phase 2, participants will track their experiences of minority stress, affect/mental health, substance use, and sexual behaviors (gender and sex of partners, types of sexual encounters, use of condoms), as well as the mechanisms of interest (isolation, gender affirmation, rumination, and internalized transphobia). Hierarchical linear modeling will be utilized to longitudinally assess predictors of the multiple epidemics (mental health, substance use, and HIV risk). Results of this study will provide much needed information for the development of future interventions to decrease these disparities in the transgender population.